The present invention relates to an apparatus for uniformly applying liquid treating media to workpiece webs. The liquid treating media are to be foamed and applied to the workpiece in foamed condition.
A basic apparatus and method for this purpose have been disclosed in German Published Application DE-OS 2,523,062 which makes the advantages of applying the treating media in foamed state very clear. The known apparatus has a container above the workpiece, and the foam is deposited within this container, and is then squeezed through a wall of the container into the workpiece.
A problem with this approach is that the direct application of the foamed medium to the workpiece does not necessarily result in proper entry of the medium into the workpiece surface; depending upon the physical surface characteristics of the workpiece, surface differences from location to location, the chemical condition of the workpiece surface and the uniformity of any chemical application (or even the condition within the confines of the workpiece), the foam bubbles will burst at different rates of speed so that different quantities of released treating liquid are available for different surface areas. In other words: application of the foam to the workpiece and squeezing of the foam into the workpiece through a side edge of the application chamber does not assure uniform entry of the foam into the workpiece.
On the other hand, it is desired that foam carrying e.g. liquid ink particles or other substances transport liquid only in minimum quantities and that this liquid be completely yielded up to (absorbed by) the workpiece.